In many applications, the requirements for the optimal performance of a metallic article vary with the location in the article. As an example, an aircraft gas turbine engine disk supports blades that are contacted by a gas stream. The disk and the supported blades are rotated at high rates by a shaft that is joined to the disk near its center. In such a gas turbine engine disk, high tensile strength and fatigue strength at moderate temperatures are required near the hub or center of the disk, and high creep strength, crack-growth resistance, corrosion/oxidation resistance, and surface-damage tolerance at higher temperatures are required near the rim of the disk. Additionally, these properties must be achieved while minimizing the weight of the disk.
Originally, the disks were made of a single material, such as a titanium-base alloy or a nickel-base alloy, with a single heat treatment. However, the different properties required in the different locations of the disk are typically not achievable with a single material in a single heat-treatment condition. Several different methods to achieve the different properties have been tried. In one method, the hub is made of one material composition and the rim is made of a different material composition joined to the hub material by an appropriate technique such as inertia welding or a co-extrusion process. The joint region may contain imperfections, arising both from the processing and from the local significant composition gradient, that limit the operating performance of the disk. In another method, the entire disk is made of one material, but the hub and rim are given different heat treatments. Precisely controlling the different heat treatments is difficult, and the properties of the hub and rim are still limited by the available properties of the selected material. In another method, the disk may be built up gradually using metal spray techniques in which the composition is slowly varied with radial position. It is difficult to control spray-produced imperfections and achieve high structural integrity with this approach. In another method, a higher performance, single-composition material is selected, but these higher performance materials are usually more costly.
The various methods all have limitations in the perfection of the metal or metals that form the disk or other part. Regardless of the technique used, the article has some fundamental limitations in that imperfections are always present that can lead to premature failure of the article. There is accordingly a need for an improved approach to making articles having property requirements that vary according to position within the article. The present invention fulfills this need, and further provides related advantages.